1. Field of the Invention
The present invention related to a boring tool, in particular a drilling and/or chisel tool, including a shank for connecting the tool with a drive tool, a stem adjoining the shank and having helical discharge grooves opening toward a stem circumference, a head provided at an end of the stem remote from the shank and having a diameter substantially corresponding to the stem diameter, the head having three radially extending recesses provided in the free end surface thereof and opening toward a head circumference, the recesses being provided with at least one hard metal bit having cutting portions extending from a central portion to at least the head circumference, and three grooves arranged between the three recesses, respectively, opening toward the head circumference, and connected with respective discharge grooves.
2. Description of the Prior Art
A drilling and/or chisel tool, further simply drill, of the type described above is used primarily for forming bores in stone, concrete and brick work. The drill has, as it has been mentioned above, a shank adapted to be received in a chuck of a drive tool. Different types of drive tools can be used with the above-described boring tool, e.g., drill hammers, all-purpose hammer tools, and chisel hammers.
The drill further includes a stem adjoining the shank and having, as it has also been described above, helical discharge grooves open at the stem circumference. The discharge groove serves for removing drillings produced by a drilling head provided at the end of the stem remote from the shank.
For forming a bore, the drilling head is provided with one or more hard metal bits which slightly project beyond the free end of the head and are arranged in recesses formed in the end surface of the head and opening toward the free end of the head.
In the drills, hard metal bits with a star-shaped arrangement of the cutting portions particularly proved themselves. These bits have a centrally arranged central portion from which hard metal inserts extend radially in three direction at substantially the same angle toward each other and at least up to the circumference of the head. Such an arrangement of hard metal inserts or cutting portions advantageously increases the drilling capacity of the drill and permits to form a bore with precise dimensions. In addition, the star-shaped arrangement of the cutting inserts provides for a quite and substantially vibration-free operation of the drill.
The drills of the type described above, have grooves which are formed in the head between the recesses in which the cutting inserts are received. These grooves extend substantially parallel to the main axis of the drill and open at the circumference of the drill. These groove are necessary for transporting of the drillings to the discharge grooves. Because of the importance of the connection of the head grooves with the discharge grooves, in the known drills, the number of the head and discharge grooves is always the same, i.e., the drill with three head grooves always has three discharge grooves.
The need to form three discharge grooves limits the production processes which can be used for producing the drills. They are limited to machining and rolling processes. By themselves, these processes can be economical. However, to insure a further economy of these processes, additional expenses for developing the necessary technical equipment are necessary and which are not always available.
Accordingly, an object of the present invention is to provide a drill with the above-discussed advantageous arrangement of the hard metal inserts, which can be economically produced by a simple forming process.